There is a need for specific spatial and temporal cDNA libraries. A complete set of libraries across developmental time periods will facilitate studies of gene function. Libraries representing different tissues and stages in development are needed to aid in the identification, localization, and characterization of the novel genes as they are discovered. This Small Business and Innovative Research (SBIR) contract will provide for the preparation of high-quality cDNA libraries from temporal and spatial embryonic mouse tissues that can be used as a source of reference.